In severe burn injuries there is destruction of the body skin covering to a degree which is related to the temperature and duration of exposure to the applied heat. As a result the protective role of the skin may be destroyed in the region of the burn to a greater or lesser extent and the damage may apply to one or more skin layers and even underlying body tissue.
Penetration of intrusive bacteria from the environment to the exposed tissue and exudation from the tissue of valuable substances may occur through the open wound, i.e. the region exposed by removal of the skin.
The heat effect which produces the burn generally also results in a destruction of the bacterial flora normally present on the skin while resistant bacteria may remain in the lower layers of tissues containing the outlets of the sweat sebaceous glands and nodules. The moist exposed wound surface is an ideal base for the propagation of intrusive bacteria.
In many burn injuries the damaged area can be extensive, i.e. the burn can cover large portions of the body area so that serious exudation losses of liquid, electrolytes and protein can occur. These fluid losses abstract significant amounts of body heat from the organism so that severe burn victims are frequently subject to serious energy and protein losses, significant nutritional, endurance and metabolic problems and the danger of infection. These problems can endure until spontaneous skin regeneration or surgical skin transplants close the wound.
In order to prevent infection of the wound by external bacteria, to limit exudative losses from the wound area and otherwise reduce the risk of complications of the type described, a sterile dressing can be applied to the wound area.
Not all conventional coverings of this nature are satisfactory. Some are incapable of preventing liquid losses by exudation, while others cannot effectively limit penetration of bacteria into the wound covering or complicate the healing process by becoming adherent to the wound tissue. In many cases replacement of the covering results in pain to the patient.
Because of these problems, it is a current practice to utilize a so-called open treatment, i.e. a treatment in which the wound remains uncovered while the environment is maintained sterile.
The natural wound exudate (e.g. plasma) is permitted to congeal over the exposed tissue and form a scab which constitutes an endogenous biological protective covering for the wound. This process has the disadvantage that it is difficult to maintain a suffiently bacteria-free environment at the body temperature of the wound. Furthermore, the procedure is impractical when the wound afflicts body portions upon which the patient may rest or which can come into contact with bedding since such contact precludes scab formation or can strip the incipient scab from the wound area, thereby causing irritation and interfering with the healing process.
Thus so-called biological coverings have been developed in a partially successful effort to overcome the disadvantages of the open-wound treatment.
While these materials have proved to be a substantial improvement over the open-wound treatment, they also have disadvantages as noted below.
Biological coverings of this type are generally composed of human or animal membranes, skin or like material, e.g. amnionic tissue, which is placed on the wound such that the layer does not adhere firmly thereto.
Before a rejection ensues, this layer is removed and, in the treatment, the process is repeated many times with fresh layers.
While each layer is in place, it performs a protective function analogous to that of the skin of the patient.
Biological coverings of this type have numerous positive characterics. For example, they favorably affect material exchange at the wound side, i.e. reduce evaporative water loss and hence heat loss from the body, and limit the exudation of fluids, electrolytes and protein, from the wound.
They also have the advantage that they reduce the bacterial count in the wound.
By replacement of the biological coverings, the bacterial count in the wound can be held below 10.sup.5 g/cm.sup.3. At the same time these biological coverings limit the possibility of infection by intrusive bacteria.
A further advantage of the use of a biological covering is that it promotes healing of the wound. The covering reduces inflammation and also limits contraction at the wound side by enabling the more rapid natural growth of skin or by creating conditions under which skin grafts can be applied sooner.
Thus the tendency to scarring and scar-tissue formation is reduced. Any information which may occur is of more limited duration and intensity.
Even the clinical effect of the use of the biological covering upon the patient is desirable. Pain is reduced to a significant degree and the afflicted body part can be immobilized or treated for shorter periods before the final treatment by way of skin grafts or the like. The skin graft operation also has a greater possibility of success.
In general the widespread use of such biological coverings reduces the death rate, even from severe burns, the hospitalization time and the cost of treatment.
Because of the aforementioned advantages, the use of biological dressings has, of late, found widespread application in many variants and, today, is perhaps the most widely accepted method of burn treatment.
However, these advantages have a concommitant disadvantage, namely the limited availability and high cost of biological wound covering materials.
Efforts have been made to use pigskin for this purpose since the structure of pigskin is most similar to that of human skin.
After disinfection the pig skin can be provided in fresh or preserved form. Since this material contains proteins, it tends to induce an immunological reaction when applied to human burn victims and must be changed every three to four days. Complications also arise with the shelf-life of the preserved material.
Thus it can be stated that, to date, conventional biological coverings have not been available in sufficient quantity and at low enough cost and with an adequate shelf-life to satisfy the increasing need for generalized use, in spite of considerable research over long periods of time.
Mention may also be made of the fact that blood substances, usually in congealed form or coagulated form, have been applied to burns and other wounds in an effort to promote the healing process. This approach has the advantage that it does not induce any immunological reaction and is theoretically an excellent approach. The fibrin, red blood corpuscles and white blood copuscles, as elements of a natural wound covering, can thus form an ideal wound dressing (see Frank Gyorgy: "Az egesek ujfajta kezelese fibrincoagulatios modszerrel" ["The Modern Treatment of Burns by the Fibrin Coagulum Process"], Orvosi Hetilap, 1949, 7, 209, and Ladanyi Jozsa: "A sebbe juttatott varrel valo kezeles hatasa a masodlagos sebgyogyulasra, hamosodara" ["The Effect of Blood Application treatment of Wounds upon Secondary Wound Healing Skin Formation"], DOTE evkonyve, 60, 1954 to 1955).
However the use of blood coagulum as a biological dressing has not found widespread application in the three decades since it was first proposed.
The various reasons for this include spontaneous solubilization of the coagulum in the wound exundates, rapid autolysis (self-solubilization) or hemolysis of the cells in situ, discoloration and the tendency of the coagulum to decompose.
Furthermore, the use of the technique invites serum hepatitis and creates an extremely moist microclimate at the wound site.
The blood components, upon application to the wound, must be held in place by gauze dressings, which create problems and the treatment of the wound is technically extremely difficult. The application of the blood components takes several steps and the prefabrication of the dressing material and its storage are impractical or impossible.